How to Read a Peptide COA: Purity and Third-Party Testing

A Certificate of Analysis, or COA, is the single most important document in research peptide sourcing. But a COA only helps if you can read it and know what it should contain. Here is a practical guide for research buyers.

What a real COA includes

A useful COA is tied to a specific batch and reports actual test results, not marketing figures. Look for:

• Batch or lot number that matches the vial you received.
• Compound name and sequence stated explicitly.
• Purity result from HPLC, expressed as a percentage.
• Identity confirmation from mass spectrometry.
• Test date and testing party, ideally an independent third-party lab.

HPLC: the purity number

High-performance liquid chromatography separates the sample into its components and measures how much of it is the target compound. The result is a percentage, and for research work you want to see 99% or higher. The chromatogram itself is informative: one dominant, clean peak is what you want. A cluster of smaller peaks means impurities, which for research reproducibility can matter as much as the headline number.

Mass spectrometry: the identity check

Purity tells you how much of the sample is one thing. Mass spec tells you whether that thing is the right thing. It measures molecular mass and confirms the sequence matches what was ordered. This catches truncated sequences, deletions, and wrong modifications that a purity percentage alone will hide. A COA with an HPLC number but no identity confirmation is only telling you half the story.

Red flags

• Generic COAs with no batch number, or the same document reused across products.
• Purity with no chromatogram or no identity method listed.
• Suspiciously round numbers like a flat 100% with no supporting data.
• No named testing party, or self-testing presented as third-party.
• Dosing or human-use language anywhere near the documentation, which signals a seller not oriented toward research.

Why third-party testing matters

A supplier testing its own product has an incentive problem. Independent, third-party analysis removes it. When a COA names an outside lab and matches your batch, you can build research on the material with confidence.

LNK Peptides provides a third-party COA on every batch, for laboratory and research use only. If you want to see an example before applying, ask and we will share one.